Delayed arming device for the proximity fuse of a bomb

ABSTRACT

A proximity type bomb fuse provided with means designed to ensure that the full arming of the fuse is delayed sufficiently for the bomb to have become separated from its point of release or propulsion by a safe distance.

[ 1 Apr. 4, 1972 iliiifie tales sent Popper [54] DELAYED ARMING DEVICE FOR THE IPRQXIMITY FUSE 0F A BOMB [72] Inventor:

.lalihin Benz Popper, Kiryat Motzkin, Israel Leonard...........................r...102/8l X [73] Assignee: The State oi Israel, Ministry of Defense, 3,066,605 12/1962 JonesI..................................102/8l X Hakiria, Tel Aviv, Israel Feb. 25, 1969 Primary ExaminerBenjamin A. Borchelt Assistant Examiner-Thomas H. Webb AltorneyKirschstein, Kirschstein & Ottinger 22 Filed:

Appl. N0.:

[57] ABSTRACT A proximity type bomb fuse provided with means designed to [30] Foreign Application Priority Data Feb- 27. 1968 Israel 29536 ensure that the full arming of the fuse is delayed sufficiently for the bomb to have become separated from its point of release or propulsion by a safe distance.

[52] U S Cl ..l02/70.2 P, 102/81 [51] Int. CL..................F42c13/00,F42c15/12, F42c 15/28 {58] .102/81, 70.2 4Claims, 2Drawing Figures Field of DELAYED ARMING DEVICE FOR THE PROXIMITY FUSE OF A BOMB This invention relates to bomb fuses and is in particular concerned with the arming mechanism of such bomb fuses.

The invention is particularly, but not exclusively concerned with proximity type bomb fuses. As used in the present specification the term bomb" refers to any form of projectile containing a high-explosive charge adapted to be launched or propelled by a mortar or other thrower or adapted to be released by an aircraft.

The detonation of a bomb by its fuse can only take place after the fuse has been fully armed. It is in all cases of vital importance to ensure that detonation of the bomb by the fuse does not take place prematurely whilst, for example, the bomb is still being carried by the aircraft or prior to its launching by the mortar or the like. For this purpose various safety mechanisms are employed, or have been proposed, so as to ensure that accidental arming of the fuse cannot take place prematurely.

It is, however, also of vital importance to ensure that, even after release or propulsion of the bomb, the detonation of the bomb by its fuse does not take place whilst the bomb is still dangerously close to the point of release or propulsion. For this purpose it is essential to ensure that the full arming of the fuse is delayed sufficiently for the bomb to have become separated from its point of release or propulsion by a safe distance,

The arming of a bomb fuse is dependent, inter alia, on the disposing of the detonator in such a position that it is capable of detonating the booster explosive of the fuse. In order therefore to carry out the full arming of the fuse it is necessary to ensure that, by the time arming is completed, the detonator has been displaced from its safe position to such a position wherein detonation of the booster explosive can take place. For the purpose of displacing the detonator it is known to provide the fuse with an impeller designed to rotate after release or launching of the bomb under the action of the air-stream, the rotation of the impeller being transmitted via suitable gearing so as to effect the required displacement of the detonator.

With proximity type fuses full arming of the fuse is also dependent upon the actuation of an electrically operated primer by an electronic signalling mechanism carried by the fuse. The actuation of this signalling mechanism can only take place when sufficient electric current is supplied thereto. The electric current is generally generated by means of an electromagnetic generator carried by the fuse and actuated by the impeller referred to above.

In order to ensure that detonation of the bomb does not take place Whilst the bomb is still dangerously close to its point of release or propulsion, arming of the fuse is delayed until the impeller has rotated a predetermined number of times. The delay period during which this predetermined number of revolutions takes place must be constant irrespective of the magnitude of the torque exerted on the impeller by the airstream. This delay period begins from the time that a torque is exerted on the impeller as a result of the propulsion or release of the bomb. As soon as this delay period has passed the impeller must be capable of free rotation so as, on the one hand, to ensure displacement of the detonator into an arming position and, on the other hand, in the case ofa proximity type fuse, to ensure generation of adequate current supply for the electronic signalling mechanism referred to above.

it is an object of the present invention to provide a delay means for a bomb fuse which ensures the effective delaying of the arming of the detonator mechanism of the fuse for a predetermined period.

According to the present invention there is provided, a delay means for a bomb fuse comprising a first element which is displaceable so as to cause movement of the detonator into an armed position, said first element being formed integrally with or coupled to a piston of a dash pot mechanism, spring biasing means for biasing the piston against fluid resistance into movement designed to allow for the displacement of the first element and a rotary screw shaft screw coupled to the piston so as to permit displacement thereof under said spring biasing only upon rotation of the screw shaft.

The screw shaft can of course be coupled to or be formed integrally with the axle of the impeller referred to above. In this case rotation of the impeller can only start upon launching or release of the bomb and therefore rotation of the screw shaft so as to allow for displacement of the piston can only begin once the bomb has been launched or released, The axial movement of the screw shaft as a result of its rotary movement always tends to take place at a greater speed than the movement of the piston under the influence of its spring biasing and against the fluid resistance. In other words, the rate of movement of the piston is only determined by the force exerted by the spring biasing means and by the resistance to movement exerted by the fluid. Thus, the time taken for the piston to be disp aced sufficiently for movement of the detonator into the armed position is always fixed, this being the predetermined delay ofthe bomb fuse.

In accordance with a preferred embodiment of the present invention the rotary screw shaft is coupled to the piston via a metallic strip which is secured adjacent to one end thereof to the piston and which has a tapped aperture formed at a position thereof spaced from said one end and substantially aligned with the axis of the piston into which aperture the r0 tary shaft is screwed, the screw threading of the rotary shaft only extending for part ofits length.

The provision of this metallic strip ensures the exertion of a braking effect on the rotation of the screw shaft. In this way, in the event that the screw shaft is formed integrally with or coupled to the axle of the impeller and the impeller operates an electro-magnetic generator, a braking effect is exerted upon the rotation of the impeller thereby preventing the generation of an adequate current supply from the generator for the arming of the electronic signalling mechanism. The arrangement is such that upon rotation of the rotary shaft, after a predetermined delay the metallic strip passes beyond the threaded portion of the rotary shaft under which circumstances the rotary shaft is freely rotatable.

One embodiment of the invention as applied to a proximity type bomb fuse will now be described by way of example and with reference to the accompanying drawings in which FIGS. 1 and 2 show partially sectioned elevations of a bomb fuse in respectively differing stages of operation.

As seen in the drawings the bomb fuse comprises a casing having a conical nose portion 1 and a substantially cylindrical body portion 2, a screw threaded portion 3 being formed at an intermediate position on the body portion 2 so as to enable the fuse to be screwed into the body ofa bomb (not shown). A rotary screw shaft 5 is coupled to an impeller 50 and extends into a cylindrical bore 6 formed in a rod 8 which depends downwardly from a piston 9 constituting part of a dash pot mechanism 10. Only the lower portion of the shaft 5 is threaded. The piston 9 comprises a circular disc portion 11 and a skirt portion 12. A peripheral recess 13 is formed in the skirt portion 12 in which is set a cup ring 14 formed of a resilient material which sealingly bears against the inner wall of the cylindrical body portion. A small aperture 15 is formed in the piston disc 11.

The rod 8 extends into a central cavity 16 formed in a detonator housing 17 located in the body portion. Three further cavities 18 are formed in eccentric equiangularly spaced positions in the housing (only one cavity being shown in the drawings). In these cavities 18 are located coiled compression springs 19 (only one shown) which bear at their lower ends on the bases of the cavities and at their upper ends against the underside of the piston disc 11. The springs 19 surround guide pins 20 (only one shown) depending from the lower end of the piston disc 11.

An elongated metal strip 21 is coupled at one end thereof to the piston disc 11 by means ofa bolt 22 which passes through an aperture formed in that end of the strip 21 and is screwed into the piston disc 11. The strip 21 has got a slight freedom of movement along the shaft of the bolt 22 between the adjacent face of the piston disc 11 and the head of the bolt 22. A threaded aperture 23 is formed at a position on the strip 21 spaced from said one end thereof and substantially aligned with the central cavity 6. The rotary screw shaft 5 is screwed into the tapped aperture 23.

Arming of the detonator mechanism (not shown) is effected when the rod 8 is displaced axially by a required predetermined amount. As can be seen from the drawings displacement of the rod 8 is effected as a result of the displacement of the piston 9 under the influence of the biasing spring 19 and against the resistance of the fluid trapped in the space adjacent the upper surface of the piston disc 11. In view of the fact, however, that the rotary screw shaft 5 is screwed into the tapped aperture 23 formed in the metal strip 21 no displacement of the piston 9 in the required direction is possible as long as the rotary shaft 5 does not rotate. Rotation of the rotary screw shaft 5 takes place as a result of the rotation of the impeller 5a and this rotation can only take place upon release or launching of the bomb. As soon as the bomb has been launched or released the rotary screw shaft 5 begins to rotate and therefore move axially into the cavity 6 the piston 11 begins to move forwardly under the influence of the biasing spring 19. This movement is however limited by the fluid resistance, referred to above, the fluid passing through the nar row aperture 15 formed in the piston disc at a limited rate. The speed of axial movement of the rotary screw shaft 5 tends to be greater than the maximum rate of displacement of the piston 9 under the influence of the spring biasing and against the fluid resistance. In consequences therefor the rate of displacement of the piston 9 and of the rod 8 will depend only on the biasing effect exerted by the spring 19 and by the rate at which the fluid can pass through the aperture 15.

At the same time, and in view of this different rate of axial displacement of the rotary shaft 5 on the one hand and the piston 9 on the other hand, the strip 21 is bent into the position shown in FIG. 2 of the drawings in which position the strip 21 effectively brakes the shaft 5 against further rotation until, as a result of the axial displacement of the piston 9, the strip 21 is restored to its substantially horizontal position whereupon rotation of the shaft 5 can continue. This procedure is continued with an intermittent braking on the rotation of the shaft 5 until the displacement of the piston 9 has proceeded so far that the tapped aperture 23 passes the threaded portion of the shaft 5 and surrounds the unthreaded portion of the shaft 5. At this point the shaft 5 can freely rotate and the piston 9 is displaced to its extreme upward position under the influence of the biasing spring 19 thereby effecting complete arming of the detonator by any suitable procedure such as, for example, the one forming the subject of our co-pending Pat. application Ser. No. 802,1 ll filed Feb. 25, 1969.

Thus the dash pot mechanism referred to above, in combination with the rotary screw shaft driven by the fuse impeller is effective in ensuring that arming of the detonator cannot take place until a predetermined delay has elapsed from the beginning of the rotation of the impeller 5a. In addition, and this is particularly relevant in the case of proximity type fuses, the particular coupling of the dash pot mechanism and the impeller, brakes the rotation of the impeller 5a and thereby prevents the impeller from acquiring a speed at which a sufficient supply of electric current can be supplied to the electronic signalling mechanism until a predetermined delay period has passed.

I claim:

l. A delay means for a bomb fuse comprising a. an element displaceable from a first position wherein it prevents movement ofa detonator into an armed position to a second position wherein said detonator is free to move into said armed position,

b. a dash pot mechanism,

. a piston forming part ofsaid dash pot mechanism, said element being associated with said piston so as to be displaceable therewith, e. spring biasing means bearing on said piston so as to bias it into movement against a predetermined fluid resistance so as to displace said element into said second position,

f. a rotary screw shaft coupled to said piston so as to inhibit movement thereof, and

g. rotary drive means coupled to said screw shaft so as to rotatably displace said screw shaft and thereby permit said displacement ofsaid piston under said spring biasing.

2. A delay means according to claim 1 which further comprises a metallic strip having a first end secured to said piston, said strip having a portion spaced from said first end and having formed therein a tapped aperture substantially aligned with an axis of said piston, said rotary screw shaft being screwed through said aperture.

3. A delay means according to claim 2 wherein said rotary drive means comprises an impeller and an impeller axle directly connected to said screw shaft.

4. A delay means according to claim 3 wherein said screw shaft includes an axial portion adjacent said impeller which is unthreaded and which is freely displaceable through said aperture. 

1. A delay means for a bomb fuse comprising a. an element displaceable from a first position wherein it prevents movement of a detonator into an armed position to a second position wherein said detonator is free to move into said armed position, b. a dash pot mechanism, c. a piston forming part of said dash pot mechanism, d. said element being associated with said piston so as to be displaceable therewith, e. spring biasing means bearing on said piston so as to bias it into movement against a predetermined fluid resistance so as to displace said element into said second position, f. a rotary screw shaft coupled to said piston so as to inhibit movement thereof, and g. rotary drive means coupled to said screw shaft so as to rotatably displace said screw shaft and thereby permit said displacement of said piston under said spring biasing.
 2. A delay means according to claim 1 which further comprises a metallic strip having a first end secured to said piston, said strip having a portion spaced from said first end and having formed therein a tapped aperture substantially aligned with an axis of said piston, said rotary screw shaft being screwed through said aperture.
 3. A delay means according to claim 2 wherein said rotary drive means comprises an impeller and an impeller axle directly connected to said screw shaft.
 4. A delay means according to claim 3 wherein said screw shaft includes an axial portion adjacent said impeller which is unthreaded and which is freely displaceable through said aperture. 